TiAlN coatings are widely used as physical vapor deposition (PVD) coatings for wear protective applications. The AlCrN system is reported to exhibit superior mechanical properties such as hardness and hot hardness, thermal and tribological properties resulting in superior application lifetime of coated parts. As commonly understood in the art, stoichiometric indices are not explicitely quoted, e.g., AlCrN stands, more precisely, for (AlyCr1-y)N (0<y<1).
U.S. Pat. No. 7,226,670 discloses a workpiece coated with a system of film layers comprising at least one film composed of (AlyCr1-y)X where X=N, C, B, CN, BN, CBN, NO, CO, BO, CNO, BNO or BNCO, the workpiece being a milling tool, a hob, a ball nose mill, a planar or a profiling cutter, a clearing tool, a reamer, an insert for turning and milling, a die or an injection mold, showing a superior wear protective performance.
U.S. Pat. No. 7,348,074 discloses coating concepts consisting of a multilayer structure with 10 layer packets. These concepts show good protective performance in drilling applications.
US patent application US 2008/0229891 discloses a multilayered coating which comprises at least one layer A comprising as material (TiAl)X, where X=N, CN, CNO or NO, or of (AlCr)X, where X=N, CN, CNO or NO, and comprising at least one layer B with (AlCrSiMe)X where X=N, CN, CNO or NO, wherein Me stands for Nb, Mo, Ta or W.
Furthermore, said US 2008/0229891 discloses that the layer structure of said at least one layer B is designed to consist of at least of two different crystalline phases. This could be for example a cubic and a hexagonal phase fraction.
In said US 2008/0229891, it is further disclosed that the thickness ratio between layer A and layer B is an important issue in the sense that coatings with thickness ratios of layer A to layer B above 1 seem to exhibit inferior performance.
All these prior art coatings show good wear protective performance for more or less special applications. It remains therefore a need to provide a wear protective coating for a broad range of different applications.